Frictional drag force act on the wetted surface of marine vehicles consumes a large portion of energy, also set an upper limit for the vehicle speed. Therefore, reducing frictional drag is critical to speeding up marine vehicles, thereby saving energy and helping to sustain the environment. Superhydrophobic (SH) surfaces have attracted much attention from both academia and industry for passively creating an air layer, trapped by its structure, to cover water vehicles, promoting slip boundary conditions and reducing frictional drag. However, the air layer within an SH surface is metastable and it tends to dissipation or non-uniform due to diffusion and pressure fluctuations, leading to negative drag reduction over time.

In this thesis, we proposed a new approach to sustain the drag reduc...[ Read more ]

Frictional drag force act on the wetted surface of marine vehicles consumes a large portion of energy, also set an upper limit for the vehicle speed. Therefore, reducing frictional drag is critical to speeding up marine vehicles, thereby saving energy and helping to sustain the environment. Superhydrophobic (SH) surfaces have attracted much attention from both academia and industry for passively creating an air layer, trapped by its structure, to cover water vehicles, promoting slip boundary conditions and reducing frictional drag. However, the air layer within an SH surface is metastable and it tends to dissipation or non-uniform due to diffusion and pressure fluctuations, leading to negative drag reduction over time.

In this thesis, we proposed a new approach to sustain the drag reduction in turbulent flow, by maintaining a stable vapor film covers the wetted surface, known as Leidenfrost effects, a physical phenomenon that droplet could levitate on an over hot surface due to a vapor film formed by the droplet rapid evaporation. However, the Leidenfrost Temperature Point (LDP), where the effect occurs, on the smooth metal surface (around 200℃) is significantly higher than its boiling temperature (100℃), may causing more energy-consuming comparing to the frictional drag. Thus, the infection of surface roughness, wettability, and porosity on LDP was studied. A certain SH surface was created with mechanical durability, thermal stability, and suitable parameters (roughness, wettability, and porosity) that could lower the LDP to 140℃.

A frictional drag measurement system was built to test both only SH surface and SH surface with Leidenfrost effect’s drag reduction rate on a water tunnel that could provide turbulent flow.